1. Technical Field
The present invention relates to a synthesis gas methanation process and apparatus.
2. Description of the Related Art
As is known, the term “synthesis gas” indicates a gas mixture consisting substantially of carbon monoxide (CO) and hydrogen (H2) and, in smaller amounts, of carbon dioxide (CO2), steam (H2O) and other compounds or impurities (also depending on the source used for its production); in general, the synthesis gas is obtained by appropriate processes of oxidative gasification of different sources (such as coal, petroleum coke, biomasses, refinery oils, different kinds of wastes, residuals of the petrochemistry industry etc.)
Among the different applications of the synthesis gas, its use is known for methanation processes, in which the synthesis gas is substantially used to produce methane.
The methanation reaction implies the reaction of H2 and CO in a molar ratio of 3:1. This reaction is performed on a catalyst and is very fast and exothermic. This is why an accurate control of the exothermicity of the reaction may be needed to have an overall feasible and efficient process.
Processes are known in which the methanation reaction is performed in a methanation reactor fed with a mixture having a molar ratio of H2:CO equal to 3:1 and is accompanied by a flow of inert matter (i.e., matter only marginally involved in the reaction) to mitigate the thermal effect of the development of reaction heat. The flow of inert matter is obtained in particular by recirculating part of the end product of the reaction to the methanation reactor with the aid of a compressor. The need to employ a compressor (generally having considerable size and a high energetic consumption) negatively affects the overall efficiency and the reliability of the process.
Furthermore, in this kind of processes the synthesis gas employed must be produced or in any case treated so as to have the desired composition and specifically the cited molar ratio H2:CO, obtained for example by partial or complete shift reaction and CO2 removal.